The standardization organization 3rd Generation Partnership Project (3GPP) has an ongoing work item Study on S2a Mobility based On GTP & WLAN access to EPC (SaMOG; see 3GPP technical report (TR) 23.852, particularly version 1.3.0 and later). This work item proposes an architecture, where a Trusted WLAN (Wireless Local Area Network) Access Network (TWAN) is connected to an EPC (Evolved Packet Core) via the S2a reference point. Further details can be found in 3GPP TS 23.402 (see particularly revision 11.4.2 or later, section 16.1).
The TWAN is further divided into functional units (see 3GPP TS 23.402 section 16.1.2 for further details). The Trusted WLAN Access Gateway (TWAG) terminates the Sea interface. The WLAN Access Network is a collection of one or more Access Points (AP). Each AP terminates the User Equipment's (UE's) IEEE 802.11 WLAN, e.g. WiFi, air link. A UE is a user device. The term User Equipment (UE) is used interchangeably herein in place of the term mobile terminal or mobile phone, or even just a terminal or device.
Parts of SaMOG have already been released in the 3GPP specifications as part of Release ii (Rel-11). SaMOG Rel-11 does not place any new requirements on the UE. As a consequence, handover with Internet Protocol (IP) address preservation between a UE's 3GPP access and WLAN access is not possible in Rel-11 In the ongoing SaMOG Rel-12 study, new requirements may be placed on the UE. In this way, it will be possible to achieve handover with IP address preservation between a UE's 3GPP access and WLAN access. However, there is still a need to find optimized solutions.